1. Field of the Invention
The present invention relates to a method and apparatus for the treatment of a waste gas containing dust and chemical contaminants. More particularly, the present invention relates to a method for cooling, dust-elimination and desulfurization of waste gases exhausted from various industrial plants as well as an apparatus for the cooling/dust-elimination and the chemical treatment, especially, desulfurization of waste gases exhausted from various industrial plants. The present invention thus provides a method and apparatus wherein a cooling/dust-eliminating device and a chemical treating device for a waste gas are integrally combined in a smaller size as a whole for attaining the treatment of the waste gas efficiently.
2. Description of the Prior Art
In prior art wet processes for desulfurizing waste gas, it is indispensable to cool the waste gas prior to the desulfurization step wherein sulfur oxide compounds are eliminated by absorption. In the prior art desulfurization apparatus, therefore, a dust-eliminating column where a circulation pump for a cooling liquid is employed is installed apart from the main desulfurization apparatus where sulfur oxide compounds are reacted and absorbed in an absorption liquid, and the cooling and dust-elimination of the waste gas are carried out in that column prior to the desulfurization. As a result of provision of such device, the apparatus for such desulfurization becomes larger as a whole and expenses for facilities and operation for the apparatus are accordingly increased. With a view to omitting such a separate dust-eliminating column, the present inventors previously proposed a method for obtaining a purged waste gas wherein a high temperature waste gas is brought into contact, in a desulfurization device for reactively absorbing sulfur dioxide, with microparticles of a cooling liquid and microparticles of an absorbing liquid to capture contaminants contained in the waste gas with these liquid microparticles while cooling the waste gas by increasing moisture. Thereafter the cooled waste gas is introduced through gas-dispersing pipes into an absorbing liquid where sulfur dioxide is eliminated by absorption (Japanese Laid-Open Patent Application No. Sho. 64-18427).
However, the above-mentioned method involves a number of problems. Firstly, the waste gas to be introduced into the absorbing liquid contains both microparticles of a cooling liquid and microparticles of an absorbing liquid, and these microparticles containing dust, HCl, HF, Al and the like contaminants removed from the waste gas dilute the absorbing liquid. Further, incorporation of these contaminants into the absorbing liquid causes deterioration of the quality of desulfurization by-products, for example, gypsum. What is more, the desulfurization performance itself of the apparatus is badly influenced by dilution of the absorbing liquid with the microparticles of the cooling liquid. Consequently, that prior art method was not completely satisfactory in these respects. So long as this point is not as yet improved, the waste gas has to be cooled and treated, prior to being introduced into the absorbing liquid, in a separate dust-eliminating device to eliminate the microparticles of a cooling liquid and dust entrained therein. Such a pretreatment is quite troublesome and makes the overall process economically unattractive.
Under these circumstances, there is a great demand to develop a new method and apparatus for the treatment of a waste gas thereby effecting the steps of cooling dust-elimination and chemical treatment of the waste gas efficiently in an apparatus which is smaller in size and capable of carrying out the steps continuously in a simple and economical manner.